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Io.Writer fix dangling pointer

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While underlying writer is Allocating writer buffer can grow in
vtable.drain call. We should not hold pointer to the buffer before that
call and use it after.
This remembers positions instead of holding reference.
This commit is contained in:
Igor Anić 2025-08-08 16:54:25 +02:00 • committed by Andrew Kelley
parent 3ee4252183
commit 6219c015d8
1 changed files with 7 additions and 6 deletions
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13
lib/std/Io/Writer.zig
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@ -317,13 +317,14 @@ test "fixed buffer flush" {
/// Calls `VTable.drain` but hides the last `preserve_len` bytes from the
/// implementation, keeping them buffered.
pub fn drainPreserve(w: *Writer, preserve_len: usize) Error!void {
const temp_end = w.end -| preserve_len;
const preserved = w.buffer[temp_end..w.end];
w.end = temp_end;
defer w.end += preserved.len;
const preserved_head = w.end -| preserve_len;
const preserved_tail = w.end;
const preserved_len = preserved_tail - preserved_head;
w.end = preserved_head;
defer w.end += preserved_len;
assert(0 == try w.vtable.drain(w, &.{""}, 1));
assert(w.end <= temp_end + preserved.len);
@memmove(w.buffer[w.end..][0..preserved.len], preserved);
assert(w.end <= preserved_head + preserved_len);
@memmove(w.buffer[w.end..][0..preserved_len], w.buffer[preserved_head..preserved_tail]);
}
pub fn unusedCapacitySlice(w: *const Writer) []u8 {